Numerous attempts have been made to devise dental aides for prosthetic work. Among these are the following U.S. Pat. No.: 1,246,408 to Fish; U.S. Pat. No. 1,726,193 to Ross; U.S. Pat. No. 2,540,555 to Slaughter, Jr.; U.S. Pat. No. 2,618,068 to Apple; U.S. Pat. No. 2,665,488 to Tobey; U.S. Pat. No. 2,910,773 to Walton; U.S. Pat. No. 3,417,471 to Mitchell; and U.S. Pat. No. 4,229,166 to Cusato et al.
Many of these devices are "paralleling instruments", which contain pins that are rigidly affixed at a 90.degree. angle to an elongated support. These devices are primarily used for placing precision attachments in laboratory models, or for making careful measurements for crown and bridgework.
These prior art devices, however, have numerous shortcomings which render them impractical in many situations encountered by dental practitioners.
For example, some of these devices can only be used for one or two teeth at a time. Others are restricted to use outside the mouth such as, for example, on plastered molds or laboratory models. Others are two bulky to be used in the posterior portions of the mouth. Another drawback is the inability to relate multiple surfaces of teeth to multiple surfaces of other teeth, such as top teeth to bottom teeth, front teeth to back teeth, and teeth on one side of the mouth to teeth on the other side of mouth.
These drawbacks are particularly troublesome when preparing teeth within the mouth for restoration with splinted teeth or multiple unit bridges. In these cases, the surfaces of the teeth must be prepared by grinding or filing, such that the bridge will have a clear "line of draw", or "path of insertion". To have a clear path of insertion, the teeth must be ground or filed such that they have a substantially truncated pyramidal shape. This will allow the bridge to slip on and off easily. Hence it is important that corresponding surfaces of different teeth are ground or filed such that there upward and inward taper is approximately the same. Equally important, is the fact that the teeth should not be over prepared in order to conserve tooth structure, and reduce the changes for later root canal therapy.